A problem that has recently cropped up, since the MX-18 update is a major delay when trying to start a file manager (Thunar, SpaceFM) or any file operation (from within Firefox or other program - loading/saving a file).

It can take 3 or 4 minutes for Thunar to load up after clicking the launcher.

If I kill the pCloud application, Thunar loads up instantly.

pCloud sets up a mounted FUSE virtual drive (I think), which I can copy files to, and I use it to store quite a bit of my digital life - so killing pCloud is a big downside to some of my general file operations.

I'm not sure whether it is a change in MX-Linux or the pCloud app has changed

Your kernel is using mq-deadline scheduler, which, in my experience, has caused slowness with the file operation (I/O) whenever I use it. It is also weird that bfq is unavailable, is your kernel a custom installed one or is it the default kernel? If possible please install liquorix kernel (which uses bfq by default), or even xanmod, and see if the situation is improved.

It looks like BFQ is now running, but there seems to be some conflicts listed that weren't in the previous output.

With the liquorix kernel in place, trying to run the pcloud.AppImage as usual, Thunar and SpaceFM are still showing a real big lag before they start up. But once they get going, they start up rapidly after that.

I'm not quite sure what to make of some of the dmesg output and whether I should just revert back to either MX 4.19 or MX 4.15 kernel or try to troubleshoot the issues here.

@spelk: The conflict warning in Liquorix is normal, it is also present on my PC, and so far I have yet seen any problem related to such warning.
Back to your case, please post the result of this command (to see how your drives are mounted):

And one more thing you can try is replacing the SATA cables and/or switching sata port. It may sound weird but in the past about 60% of problems related to I/O lags I have faced were solved by doing so.

I see that smartctl report some errors with your sdb drive (Western Digital Black). Is there any chance that you put the data for syncing on that drive (or the pcloud appimage)? If so you can put data and the appimage file on another drive and see if it is improved. If not I recommend replacing the sata cables and running fsck on your drive. Remember that before running fsck, you should unmount the drive first, and you may need to run it as root.

By the way, there may be another issue that is really difficult to detect, and it is related to the PSU. I once had a PC that lagged and crashed frequently, running tests on RAM and HDD showed nothing, replacing sata cables had no effect. Only when I replaced the PSU that everything run smoothly again.

And one more thing, if possible considering replacing the drive, because whenever SMART shows any error, it is always not a good sign.

As an update to this, the issue is still happening.. and it's happening across multiple MXLinux installations on different hardware (desktop, laptop) running different kernels (liquorix 4.19 and 4.19).

With pCloud.AppImage running, Thunar seems to take 30-40 seconds sometimes more to load up. This happens running Thunar from the File Manager panel launcher "exo-open --launch FileManager %u" and also if I specifically add Thunar to the panel "thunar %F".

If I kill the pCloud.AppImage running in the task tray, Thunar will instantly open, without a problem.

(these findings are on a different piece of hardware to the initial request for help, but the symptoms are the same - and I'm trying to work out what settings with the FUSE mounting system is causing Thunar to stall for a long time before being able to load up)

I think pCloud uses the FUSE system and Investigating around the topic, findmnt reports these

But this points to an empty directory as far as I can tell, and I'm not sure what role gvfs-fuse plays in this pantomime.

I'm not entirely sure why SpaceFM now works ok with pCloud but Thunar does not. There must be some issue with reading/evaluating the pCloud mounted cloud drive inside of Thunar as it opens up.

Interestingly, if you run Thunar as sudo, it opens instantly, shows the pCloudDrive as a device, but selecting it shows it as empty. Even though it is actually connected and has content on it. So sudo Thunar isn't connecting to the cloud drive - I'm guessing because the AppImage is running under my user profile.

I'd skip Thunar and just use SpaceFM as a workaround, but a lot of programs use Thunar as their default mechanism for loading/saving files and/or selecting directories.

I'm sure its just an small issue with Thunar not being able to do something on the fuse mounted drive.. but I'm not knowledgeable enough about that mechanism to elucidate the issue yet.